A Wire Bonder is an automatic machine with which semiconductor chips are wired to a substrate after mounting. The Wire Bonder has a capillary which is clamped to the tip of a horn. The capillary serves to secure the wire to a connection point on the semiconductor chip and to a connection point on the substrate as well as to guide the wire between the two connection points. The position of the connection points is determined prior to bonding by means of an image recognition system so that the capillary impinges at the right location on the connection point. However, during operation, a problem exists in that the distance between the capillary and the optical axis of the image recognition system can change in an unpredictable manner because of thermal effects. The distance therefore has to be continuously re-calibrated.